1. Field of the Invention
The present invention relates to a combined marine mooring and cargo transfer system for use for example between a supertanker offshore and a pipeline to shore based facilities.
The invention relates to a relatively stable floating pipeline which rises from the ocean floor to a position well above the hull of the ship. It is held in a relatively vertical position by the buoyant force of the water and has articulating ability to weathervane. It will conform to all of the movements of the ship while limiting its horizontal movements.
The present invention also relates to the method of attaching the top of the floating riser to the mooring pedestal on the bow of the ship by means of a mooring winch which overcomes the buoyant force of the riser. The attachment allows fluid to flow between the ship and the riser while performing the mooring function.
The invention also relates to the elements of articulation such as: flow through pins in universal joints, and heavy duty swivel joints which have the structural ability to accommodate the mooring forces as well as conduct fluid flow.
The method of cushioning the tension and compression of the mooring loads on the riser is included in the invention.
The method of using an anchor mat which is capable of attaching itself to the bottom as well as removing itself back to a floating condition is also included.
The purpose of the present invention is to increase the ability to operate in rough sea conditions, increase safety for the workers, decrease the possibility of spillage, decrease maintenance, reduce the time necessary for mooring and cargo line connections, decrease the time of departure, simplify required operating facilities, reduce manpower requirements, reduce operational cost, and in general to relieve or eliminate many other problems in the conventional systems.
2. Description of the Prior Art
One of the major problems facing the superport operations today is that of attaching the mooring lines in rough sea conditions. The most popular techniques involve the attachment of mooring lines to a relatively active anchor buoy. This is accomplished by a boat which picks up the mooring lines. A man from the boat boards the buoy and makes the attachment. Or he must attach the mooring lines from the ship to floating mooring lines from the buoy. Seas that have wave heights of 5 feet or better make this attachment method dangerous or it might not be attempted at all. Delays because of weather limit productivity and is very expensive. Also, the most popular systems involve floating hoses which connect the flow lines on the ocean bottom to the cargo piping on the ship. These hoses are also handled by boats that position them next to the ship, where they are lifted aboard by cranes on the ship. Obviously, this operation becomes hazardous in rough sea conditions. These hoses then must be hand connected to the ship's piping system. This operation requires many men, boats and time.
Floating hoses are very expensive and must be changed frequenty because of the high stress exerted on them by the action of the waves. Another problem of floating hoses is that they can become pinched between the ship and the buoy, should the ship drift into the buoy. Such pinching activity normally requires the changing of the hoses or may even cause spillage.
The single point mooring (SPM) system is considered by many to be the safest and most economical method of offshore superport operations. It is not new in the art since it has been in operation since 1959.
The elements of the SPM system is a floating buoy which is anchored to the ocean floor and serves as a mooring buoy. A flow line from shore facilities is located on the sea bottom being connected to a flexible hose in the area of the buoy anchor. It extends to the surface where it attaches to floating hoses which are connected to the ship's cargo lines. This arrangement allows the ship to weathervane around the anchor while the cargo is being transferred.
Typical examples of the prior art in the offshore tanker cargo transfer are the following U.S. Patents:
______________________________________ Patent No. Date Issued Inventor ______________________________________ 3,017,934 Jan. 23, 1962 A. D. Rhodes, et al. 2,955,626 Oct. 11, 1960 A. C. Hartley 3,360,810 Jan. 2, 1968 B. E. Busking 3,372,049 Mar. 12, 1968 W. T. Manning 3,409,055 Nov. 5, 1968 P. J. Bily 3,407,416 Oct. 29, 1968 A. A. Brickhouse 3,434,442 Mar. 25, 1969 W. T. Manning ______________________________________
However, none of these patents disclose a relatively solid but flexible riser which is capable of structurally mooring the vessel while performing the function of cargo transfer in one manipulation.